The present invention relates to a voltage regulator for controlling electric power generated by an alternator coupled to a vehicle engine to maintain a battery charging voltage at a constant level.
Voltage regulators of the type described have a switching means for turning on and off a current flowing through the rotor coil of an alternator to control electric power generated thereby. More specifically, the voltage regulator controls electric power generated by the alternator dependent on an increase or reduction in the electric load coupling to the alternator to increase or reduce an output current therefrom in order to maintain a constant voltage for charging a battery.
Voltage regulators include battery-sensing type voltage regulators and alternator-sensing type voltage regulators. The battery-sensing type voltage regulator directly senses a battery charging voltage for keeping the latter at a constant level. The alternator-sensing type voltage regulator maintains an output voltage from the alternator at a level slightly higher than a battery charging voltage, taking into account a voltage drop across a charging output line, and is simpler in arrangement than the battery-sensing type voltage regulator.
The recent trend in automotive technology is toward much more electric parts equipped in automobiles, and hence the alternator on automobiles is subjected to a greatly varying electric load dependent on the manner in which the electric parts are used. Therefore, the voltage regulator is required to vary the output current from the alternator to a large extent dependent on the electric load so as to keep the battery charging voltage constant. While the alternator-sensing type voltage regulator allows a constant output voltage from the alternator, it produces a large variation in the voltage drop across the charging output line, with the result that an actual battery charging voltage will vary beyond an allowable level, thus charging or discharging the battery excessively.
The battery-sensing type voltage regulator does not suffer from any variation in the battery charging voltage due to a voltage drop across the charging output line since the voltage regulator directly senses the battery charging voltage. However, with a battery charging voltage preset for a normal load condition, the battery tends to be charged or discharged excessively when a large electric load is used for a long period of time while the vehicle is running at low speed or when only a small electric load is used for a long period of time while the vehicle is travelling at high speed.